Enforcing promotional goods ship with the item that triggered their addition to a sales order

Hello Everybody

We are facing a business requirement for Promotional Goods pricing modifier so that a free item is included in the sales order with some shippable and billable other items.

e.g. if you buy X tyres you get a branded Tee-Shirt or cap for free.

However we would like to know whether there is any mechanism to enforce that the free/promotional good item always gets shipped if and only if the tires are with it.

Putting both lines in a ship set would do so?

Is there any way to automate addition of the promotional good in a ship set with the item(s) that triggered its addition to sales order or is it only a manual process and user decision?